A plant for turning seawater into freshwater is constructed in the vicinity of a seashore in order to obtain drinking water on an island and a desert region where there is only a small amount of precipitation. Furthermore, seawater is, for example, prime water for a plant making salt. In this type of seawater treatment plant, it is necessary to introduce seawater into equipment for turning seawater into freshwater.
Furthermore, in a nuclear power generation plant, a great amount of cooling water is required. In a case where such a power generation plant is installed in the vicinity of a seashore, seawater is used for cooling, and seawater is introduced as in the abovementioned plant.
Therefore, conventionally, in such a seawater treatment plant and a power generation plant, seawater was taken in by a water intake structure shown in "FIG. 13" to FIGS. 13A and 13B and FIG. 14.
In the water intake structure illustrated in the same drawing, a water reservoir 1 is installed in the vicinity of a seashore, a water collecting portion 2 is installed on the sea bottom, and a water conveyance pipe 3 is used to connect the water reservoir 1 to the water collecting portion 2, wherein seawater taken into the water reservoir 1 is pumped up by a pump 4 and is distributed to various kinds of facilities.
A number of water intake pipes 5 protruding toward both sides of the water conveyance pipe 3 are provided at the water collecting portion 2. A number of through holes are provided on the respective water intake pipes 5, and a synthetic resin net or unwoven cloth is wound on the outer circumference thereof in order to prevent earth and sand from invading.
In such a water intake structure, usually, a water conveyance pipe 3 is buried by a driving method or a dig-sink method.
However, in such a conventional burying method of a water conveyance pipe 3, there existed the following shortcomings and problems in the technical aspects as described below.
That is, when burying a water conveyance pipe 3 by a driving method or a dig-sink method, various limitations in working exist, resulting from the surrounding vicinity of the place directly above the burying position of the water conveyance pipe 3 being exclusively occupied.
For example, in work carried out by the driving method in a sea, since seawater is to be shut out, this causes a hindrance in sea transportation and makes it necessary to guarantee fishery rights.
Therefore, the present inventors developed a method for constructing a water intake pipe by utilizing a shield tunnel in order to solve these shortcomings and problems. Since places directly above the water intake pipe are not exclusively occupied if a water intake pipe is constructed by a shield construction method, no problems such as ocean pollution, etc. will occur.
However, a segment used for a conventional shield construction method is, generally, constructed of a segment body 6 made of steel reinforced concrete as shown in FIG. 14, wherein a plurality of segment bodies 6 are circumferentially connected to each other and are assembled to be cylindrical, and the assembled cylindrical bodies are connected one after another in the lengthwise direction.
The respective segment bodies 6 are provided with back-filling pores 7 penetrated in the thickness direction thereof, into which a back-filling material is supplied, and the back-filling pores 7 are clogged by a detachable plug packing 8.
The segment bodies 6 are connected to each other in the axial direction by bolts and nuts 10 with a packing put therebetween in a joint box 9 secured at the ends in the lengthwise axial direction, and a sealing material 11 and a caulking material 12 are caused to intervene between the end faces of the segment bodies 6.
As the segments are assembled, the plug packing 8 is detached, and a back-filling material 13 is supplied through the back-filling pores 7 between the outer circumferential surface of the segment bodies 6 and the driven surface of the ground, wherein a secondary coating layer 14 is formed on the inner circumferential side of the segment bodies 6.
With the segments thus constructed, external water is prevented from invading by causing the sealing material 11 to intervene, and supplying the back-filling material 13 into the backside, and internal water is thus prevented from leaking outside. Principally, such segments are constructed so that a water stop function is secured. Therefore, such segments do not have the feature of a water intake pipe for intake of seawater, and such types of segments could not be used for intake of water as they are.
The present invention was developed in view of such shortcomings and problems, and it is therefore an object of the invention to provide a segment for a water intake tunnel having a feature suitable for intake of water.